According to researchers at Columbia University, people with high levels of HDL cholesterol (the “good” form) are 60 percent less likely to develop AD. The researchers followed 1,130 seniors with no history of memory loss or dementia and measured their cholesterol levels every 18 months for four years. When the researchers compared the cholesterol levels of study participants with and without Alzheimer’s, they found that those with the highest HDL counts, greater than 55 mg/dL, had about a 60 percent reduced risk of developing the disease compared to those whose levels were less than 39 mg/dL.

Their findings support the theory that high levels of HDL cholesterol are correlated with lower incidence of AD. The study was published earlier this week in the Archives of Neurology and sheds more light on the interactions between cholesterol and AD.

Apolipoprotein E (apoE), as readers of this blog will recall, participates in the mobilization and distribution of cholesterol among various tissues of the body, including the brain. In humans, there are three common isoforms of apoE: apoE2, apoE3 and apoE4. ApoE4 differs from apoE3, the most common isoform of apoE. A single e4 allele is sufficient to increase the risk of developing atherosclerosis, and also Alzheimer’s disease. The e4 allele results in slightly elevated plasma LDL cholesterol levels and a small but significant decrease in plasma HDL levels. HDL is one of the major carriers of protein in and out of the brain, and also binds to beta-amyloid.

This finding further advances the idea that the interplay between cholesterol, cholesterol-carrying proteins such as apoE and HDL, and beta-amyloid may be critical in the development of Alzheimer’s disease. This study has important strengths. It is a prospective cohort study designed for the diagnosis of cognitive decline that has complete clinical and neuropsychological evaluation at each interval.

Guidelines recommend that men raise HDL levels that are less than 40 mg/dL and that women increase HDL numbers less 50 mg/dL. An HDL of 60 mg/dL or higher is optimal.